Coil

ABSTRACT

A coil which maintains a balance of a parasitic capacitance and has a structure that can be multilayered. The coil is stacked with a structure which includes winding wire portions formed of a wire wound for several turns in a plane in each layer, wherein winding wire portions in each layer include a first winding portion formed by performing a single turn of winding in each layer in a same winding direction from a bottom layer to an uppermost layer, and a second winding portion formed by performing a single turn of winding in each layer in a same winding direction from the uppermost layer to the bottom layer, and the winding directions of the first and second winding portions are identical to each other and the first winding portion and the second winding portion are joined in the uppermost layer or the bottom layer.

This is a Divisional Application of application Ser. No. 14/554,702filed Nov. 26, 2014, which claims priority to JP2014-212678 filed Oct.17, 2014 and JP2013-246455 filed Nov. 28, 2013. The disclosures of theprior applications are hereby incorporated by reference herein in theirentirety.

The present invention relates to a coil for transmitting power orreceiving power which is used in a contactless power supply apparatusfor supplying power in a contactless manner.

BACKGROUND

In recent years, the contactless power transmission is attractingattentions with which the power is transmitted in a contactless mannerfrom the power transmitting side to the power receiving side. Forexample, the contactless charging device is increasingly developed whichuses the technique of contactlessly transmitting power in order tocharge the battery mounted in an electric vehicle. In such a contactlesscharging device, a spiral coil formed in a plane is mostly used as thecoil for transmitting power or receiving power. However, as the coil fortransmitting power or receiving power, in order to obtain sufficientproperties, there is a problem that the size of coil becomes large.

As a means to solve such a problem, Patent Document 1 has disclosed acoil with a double layered structure which is obtained by connecting aspiral coil formed in the first layer and a spiral coil formed in thesecond layer in series. The spiral coil is usually used by disposing amagnetic plate made from a magnetic material and a metallic plate (suchas an aluminum plate and a copper plate) made from a nonmagneticmetallic material on the back side of the coil, and thus a parasiticcapacitance is generated between the conductor of the coil and themetallic plate. In addition, in the coil with a double layeredstructure, the distance between the conductor of the spiral coil formedin the first layer and the metallic plate is different from that betweenthe conductor of the spiral coil formed in the second layer and themetallic plate, and thus the parasitic capacitance generated between theconductor of the spiral coil formed in the first layer and the metallicplate will differ from that generated between the conductor of thespiral coil formed in the second layer and the metallic plate.

PATENT DOCUMENT

Patent Document 1: JP-A-2011-86890

SUMMARY

Therefore, when the coil with a double layered structure which has beendisclosed in Patent Document 1 is used in the power transmission, thevoltage to ground of the metallic plate sometimes is increased under theinfluence of the imbalance of the parasitic capacitance.

In this respect, the present invention aims to provide a coil which iscapable of maintaining the balance with the parasitic capacitance of themetallic plate and has a structure that can be configured multilayered.Further, the present invention also aims to provide a coil with amultilayered structure having good productivity.

In order to solve the problems mentioned above, the coil according tothe present invention is a coil with a stacked structure which isprovided in each layer with a winding wire portion formed of a wirewound for several times in a plane, wherein the winding wire portion ineach layer includes a first winding portion formed by for performing asingle turn of winding in each layer in a same winding direction from abottom layer to an uppermost layer and a second winding portion formedby performing a single time of winding in each layer in a same windingdirection from the uppermost layer to the bottom layer, and the windingdirections of the first winding portion and the second winding portionare identical to each other and the first winding portion and the secondwinding portion are joined in the uppermost layer or the bottom layer.

In this structure, each part of the wire can be dispersedly disposed inthe winding wire portion in each layer. That is, the parts forming thewinding wire portion of each layer from the bottom layer to theuppermost layer can be dispersed between one end portion and the otherend portion of the wire, and a bias that the winding wire portion in thebottom layer is disposed at a side close to one end portion of the wireand the winding wire portion in the uppermost layer is disposed at aside close to the other end portion of the wire will not occur. Thus, animbalance of a parasitic capacitance with a metallic plate due to astructure of the coil is also inhibited. Further, as the winding processin each layer can be performed in parallel, the coil with a multilayeredstructure can be effectively produced.

Preferably, the winding wire portions in the adjacent upper and lowerlayers face to each other through an insulating member. According tothis structure, the winding wire portions in the adjacent upper andlower layers are separated, and thus a loss due to the closing effectamong these winding wire portions can be eliminated.

Preferably, the insulating member may be a planar member provided with aslit, and the wires of the winding wire portions in the adjacent upperand lower layers are joined via this slit.

The winding wire portion can be effectively formed in each layer bydisposing a slit on the planar member. In addition, the wires are joinedvia the slit between the winding wire portions in the adjacent upper andlower layers, and thus the wire will not be provided with an excesspressure.

In addition, the coil of the present invention is a coil with a stackedstructure and includes a bobbin which includes a plate portion forseparating a wire-accommodating portion in each layer, and a windingwire portion which is formed of a wire wound several times in a planeand is accommodated in the wire-accommodating portion in each layer,wherein the winding wire portion includes a first winding portion formedby performing a single turn of winding in each layer in a same windingdirection from a bottom layer to an uppermost layer of thewire-accommodating portion, and a second winding portion formed byperforming a single turn of winding in each layer in a same windingdirection from the uppermost layer to the bottom layer of thewire-accommodating portion with a single turn for each layer, and thewinding directions of the first winding portion and the second windingportion are identical to each other and the first winding portion andthe second winding portion are joined in the uppermost layer or thebottom layer of the wire-accommodating portion.

In this structure, each parts of the wire can be dispersedly disposed inthe winding wire portion of each layer which is accommodated in thewire-accommodating portion. Thus, an imbalance of a parasiticcapacitance due to a structure of the coil is inhibited. Further, sincethe wire-accommodating portion in each layer is separated by the plateportion, a loss due to a closing effect between the winding wireportions in the adjacent upper and lower layers can be eliminated.

In addition, since the winding process of the wire-accommodating portionin each layer can be performed in parallel, the coil with a multilayeredstructure can be effectively produced.

Preferably, the plate portion may include a slit, and the wires of thewinding wire portions which are accommodated in the wire-accommodatingportions in the adjacent upper and lower layers are joined via thisslit.

The winding wire portion accommodated in the wire-accommodating portionof each layer can be effectively formed by disposing such a slit. Inaddition, the wires are joined via the slit between the winding wireportions accommodated in the wire-accommodating portions in the adjacentupper and lower layers, and thus the wire will not be provided with anexcess pressure.

According to the coil with a multilayered structure according to thepresent invention, a coil with a multilayered structure can beeffectively prepared in which a distribution of a parasitic capacitancewith a metallic plate is more uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic exploded view showing the structure of the coilwith double layers according to the first embodiment.

FIG. 2 is a sectional view showing the section of the coil with a doublelayered structure according to the first embodiment.

FIG. 3 is a schematic exploded view showing the structure of the coilwith double layers according to the second embodiment.

FIG. 4 is a sectional view showing the section of the coil with a doublelayered structure according to the second embodiment.

FIG. 5 is a sectional view showing the section of the slit.

FIG. 6 is a sectional view showing the section of the coil with a threelayered structure.

FIG. 7 is a circuit diagram showing the principle part of thecontactless power transmission circuit.

FIG. 8 is a sectional view showing the structures of the powertransmitting coil and the power receiving coil.

FIG. 9 is a sectional view showing the structures of the powertransmitting coil and the power receiving coil.

DESCRIPTION OF REFERENCE NUMERALS

-   1. the bobbin-   1 a, 1 b, 1 c. the plate portion-   2. the wire-   2 a, 2 b, 2 c. the winding wire portion-   3. the slit-   4. the chamfer portion-   10, 30. the power transmitting coil-   11, 21, 31 a, 31 b, 41 a, 41 b. coil-   12, 22, 32, 42. the magnetic member-   13, 23, 33, 43. the metallic plate-   20, 40. the power receiving coil

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments for carrying out the present invention will be explainedin detail with reference to the accompanying drawings. Further, thepresent invention is not limited to these embodiments to be describedbelow. In addition, the same reference numeral refers to the sameelement or an element having the same function, and repeateddescriptions will be omitted in the following description.

FIG. 1 is a schematic exploded view showing the coil with a doublelayered structure according to the first embodiment with each layerbeing separated from each other, and FIG. 2 is a sectional view showingthe section of the coil along the line a-a′. The coil with a doublelayered structure includes a winding wire portion 2 a of the first layer(the bottom layer) and a winding wire portion 2 b of the second layer(the uppermost layer) both of which are formed by winding a wire 2. Thebobbin 1 of the coil has a wire-accommodating portion of the first layer(the bottom layer) and a wire-accommodating portion of the second layer(the uppermost layer) on the plate portion 1 a on the side of the uppersurface. In addition, the winding wire portion 2 a of the first layer(the bottom layer) is accommodated in the wire-accommodating portion ofthe first layer (the bottom layer), and the winding wire portion 2 b ofthe second layer (the uppermost layer) is accommodated in thewire-accommodating portion of the second layer (the uppermost layer).Herein, the wire-accommodating portion refers to a space to accommodatethe winding wire of each layer. That is, in the present embodiment, twowire-accommodating portions are provided, one of which the winding wireportion 2 a of the first layer is accommodated and the other of whichthe winding wire portion 2 b of the second layer is accommodated.

In the coil with a double layered structure, the winding wire in theinnermost periphery of the winding wire portion 2 a of the first layer(the bottom layer) and the winding wire in the innermost periphery ofthe winding wire portion 2 b of the second layer (the first circle ofthe winding wire) (the uppermost layer) are joined (directly connected),and the second circle of winding wire from the innermost periphery ofthe winding wire portion 2 a (the second circle of the winding wire) andthe second circle of winding wire from the innermost periphery of thewinding wire portion 2 b (the second circle of the winding wire) arejoined (directly connected). Similarly below, the winding wires with thesame winding number are joined (directly connected) to each other. Inaddition, the first circle of winding wire and the second circle ofwinding wire are joined in the second layer (the uppermost layer), andthe second circle of winding wire and the third circle of winding wireare joined in the first layer (the bottom layer). Similarly below, thewinding wire of each winding number is joined to the winding wire of thenext winding number in the first layer (the bottom layer) or the secondlayer (the uppermost layer).

That is, in the coil according to the present invention having astructure of n layers (n represents an integer that is equal to orlarger than 2), the winding wires of circle No. j (j refers to aninteger that is equal to or larger than 1) in each layer are joinedbetween the adjacent layers, and the winding wire of circle No. j andthe winding wire of circle No. (j+1) are joined in the first layer (thebottom layer) or layer No. n (the uppermost layer). Further, all thewires forming the winding wire portion in each layer are wound in thesame winding direction. Thus, a magnetic field will be generated that issubstantially the same as that generated when n layers of spiral coilsare stacked.

Next, the winding process for forming the winding wire portion 2 a ofthe first layer (the bottom layer) and the winding wire portion 2 b ofthe second layer (the uppermost layer) will be explained. The windingprocess may be started by winding either one of the winding wire portion29 of the first layer (the bottom layer) and the winding wire portion 2b of the second layer (the uppermost layer), but in the followingexplanation, the winding process is started by winding the winding wire2 a of the first layer (the bottom layer). Further, in the followingwinding process, all the winding processes are performed in the samedirection.

First of all, the winding process from the first circle of the windingwire portion 2 a of the first layer (the bottom layer) to the firstcircle of the winding wire portion 2 b of the second layer (theuppermost layer) will be explained. In this process, the winding processfor forming the first circle of winding wire a1 in the winding wireportion 2 a of the first layer (the bottom layer) is performed at first,and then the winding process for forming the first circle of windingwire b1 in the winding wire portion 2 b of the second layer (theuppermost layer) is performed. As such, a single turn of winding isperformed from the bottom layer to the uppermost layer in sequence, andthereby a circle of winding wire is formed in the winding wire portionof each layer. Hereinafter, this process is referred to as the firstwinding process, and the part formed in the first winding processbecomes the first winding portion in which a single turn of winding isperformed for each layer in the same winding direction from the bottomlayer to the uppermost layer.

Next, the winding process from the second circle of the winding wireportion 2 b of the second layer (the uppermost layer) to the secondcircle of the winding wire portion 2 a of the first layer (the bottomlayer) will be explained. In this process, the winding process forforming the second circle of winding wire b2 in the winding wire portion2 b of the second layer (the uppermost layer) is performed at first, andthen the winding process for forming the second circle of winding wirea2 in the winding wire portion 2 a of the first layer (the bottom layer)is performed. As such, a single turn of winding is performed from theuppermost layer to the bottom layer in sequence, and thereby a circle ofwinding wire is formed in the winding wire portion of each layer.Hereinafter, this process is referred to as the second winding process,and the part formed in the second winding process becomes the secondwinding portion in which a single turn of winding is performed for eachlayer in the same winding direction from the uppermost layer to thebottom layer.

In this way, the first circle of winding wire a1 in the winding wireportion 2 a of the first layer (the bottom layer) and the first circleof winding wire b1 in the winding wire portion 2 b of the second layer(the uppermost layer) are formed by performing the first windingprocess, and then the second winding process is performed, and therebythe second circle of winding wire b2 in the winding wire portion 2 b ofthe second layer (the uppermost layer) and the second circle of windingwire a2 in the winding wire portion 2 a of the first layer (the bottomlayer) are formed. Similarly below, the first winding process and thesecond winding process are repeated alternatively so that the third tosixth circle of winding wires a3 to a6 in the winding wire portion 2 aof the first layer (the bottom layer) and the third to sixth circle ofwinding wires b3 to b6 in the winding wire portion 2 b of the secondlayer (the uppermost layer) are formed. The thus formed winding wireportion 2 a of the first layer (the bottom layer) and the winding wireportion 2 b of the second layer (the uppermost layer) become windingwire portions that are wound 6 circles in a plane. The planar windingwire portion 2 a faces the winding wire portion 2 b in a direction fromthe bottom layer to the uppermost layer. That is, when viewed from adirection from the bottom layer to the uppermost layer, the winding wireportion 2 a and the winding wire portion 2 b are formed so as to overlapeach other with winding wires of the same winding number.

As described above, the coil with a double layered structure shown inFIG. 1 and FIG. 2 according to the first embodiment is formed byperforming the first winding process and the second winding process eachfor three times. In other words, the first circle of winding wire a1 inthe winding wire portion 2 a of the first layer (the bottom layer) andthe first circle of winding wire b1 in the winding wire portion 2 b ofthe second layer (the uppermost layer) are formed by performing thefirst winding process for the first time, and then the second circle ofwinding wire b2 in the winding wire portion 2 b of the second layer (theuppermost layer) and the second circle of winding wire a2 in the windingwire portion 2 a of the first layer (the bottom layer) are formed byperforming the second winding process for the first time. Then, thethird circle of winding wire a3 in the winding wire portion 2 a of thefirst layer (the bottom layer) and the third circle of winding wire b3in the winding wire portion 2 b of the second layer (the uppermostlayer) are formed by performing the first winding process for the secondtime, and then the fourth circle of winding wire b4 in the winding wireportion 2 b of the second layer (the uppermost layer) and the fourthcircle of winding wire a4 in the winding wire portion 2 a of the firstlayer (the bottom layer) are formed by performing the second windingprocess for the second time. Next, the fifth circle of winding wire a5in the winding wire portion 2 a of the first layer (the bottom layer)and the fifth circle of winding wire b5 in the winding wire portion 2 bof the second layer (the uppermost layer) are formed by performing thefirst winding process for the third time, and then the sixth circle ofwinding wire b6 in the winding wire portion 2 b of the second layer (theuppermost layer) and the sixth circle of winding wire a6 in the windingwire portion 2 a of the first layer (the bottom layer) are formed byperforming the second winding process for the third time.

The winding wire portions 2 a and 2 b can also be wound in any one ofshapes such as a circle, an oval, a substantial quadrangle or the like.In addition, a wire obtained by covering the Litz wire with aninsulating tube may also be used as the wire 2.

FIG. 3 is a schematic exploded view showing the coil with a doublelayered structure according to the second embodiment with each layerbeing separated from each other, and FIG. 4 is a sectional view showingthe section of the coil along the line A-A′. The coil with a doublelayered structure includes a winding wire portion 2 a of the first layer(the bottom layer) and a winding wire portion 2 b of the second layer(the uppermost layer), both of which are formed by winding a wire 2. Inaddition, a bobbin 1 of the coil has a wire-accommodating portion of thefirst layer (the bottom layer) on a plate portion 1 b on the side of thebottom surface (between the plate portion 1 a and the plate portion 1 b)and a wire-accommodating portion of the second layer (the uppermostlayer) on the plate portion 1 b on the side of the upper surface. Thatis, besides the difference about plate portion 1 a, the bobbin 1 in thecoil with a double layered structure according to the second embodimentfurther differs from that of the first embodiment in that a plateportion 1 b is provided. Further, the winding wire portion 2 a of thefirst layer (the bottom layer) is accommodated in the wire-accommodatingportion of the first layer (the bottom layer) and the winding wireportion 2 b of the second layer (the uppermost layer) is accommodated inthe wire-accommodating portion of the second layer (the uppermostlayer).

In the coil with a double-layered structure, the winding wire in theinnermost periphery of the winding wire portion 2 a of the first layer(the bottom layer) and winding wire in the innermost periphery of thewinding wire portion 2 b of the second layer (the uppermost layer) (thefirst circle of the winding wire) are joined (directly connected), andthe second winding wire from the innermost periphery of the winding wireportion 2 a (the second circle of the winding wire) and the secondwinding wire from the innermost periphery of the winding wire portion 2b (the second circle of the winding wire) are joined (directlyconnected). Similarly below, the winding wires with the same windingnumber are joined (directly connected) to each other. In addition, thefirst circle of the winding wire and the second circle of the windingwire are joined in the second layer (the uppermost layer), and thesecond circle of the winding wire and the third circle of the windingwire are joined in the first layer (the bottom layer). Similarly below,the winding wire of each winding number in the first layer (the bottomlayer) or the second layer (the uppermost layer) is joined to thewinding wire of the next winding number.

That is, in the coil according to the present invention having astructure of n layers (n represents an integer that is equal to orlarger than 2), the winding wires of circle No. j (j refers to aninteger that is equal to or larger than 1) in each layer are joinedbetween the adjacent layers, and the winding wire of circle No. j andthe winding wire of circle No. (j+1) are joined in the first layer (thebottom layer) or layer No. n (the uppermost layer). Further, all thewires forming the winding wire portion in each layer are wound in thesame winding direction. Thus, a magnetic field will be generated that issubstantially the same as that generated when n layers of spiral coilsare stacked.

Next, the winding process for forming the winding wire portion 2 a ofthe first layer (the bottom layer) and the winding wire portion 2 b ofthe second layer (the uppermost layer) will be explained. The windingprocess may be started by winding either one of the winding wire portion2 a of the first layer (the bottom layer) and the winding wire portion 2b of the second layer (the uppermost layer), but in the followingexplanation, the winding process is started by winding the winding wire2 a of the first layer (the bottom layer). Further, in the followingwinding process, all the winding processes are performed in the samedirection.

First of all, the winding process from the first circle of the windingwire portion 2 a of the first layer (the bottom layer) to the firstcircle of the winding wire portion 2 b of the second layer (theuppermost layer) will be explained. In this process, the winding processfor forming the first circle of winding wire a1 in the winding wireportion 2 a of the first layer (the bottom layer) is performed at firstand then the winding process for forming the first circle of windingwire b1 in the winding wire portion 2 b of the second layer (theuppermost layer) is performed. As such, a single turn of winding isperformed from the bottom layer to the uppermost layer in sequence, andthereby a circle of winding wire is formed in the winding wire portionof each layer. Hereinafter, this process is referred to as the firstwinding process, and the part formed in the first winding processbecomes the first winding portion in which a single turn of winding isperformed for each layer in the same winding direction from the bottomlayer to the uppermost layer. Further, when the wire 2 is moved from thefirst circle in the winding wire portion 2 a of the first layer (thebottom layer) to the first circle in the winding wire portion 2 b of thesecond layer (the uppermost layer), it passes through a slit 3 providedin the plate portion 1 b and enters into the wire-accommodating portionof the second layer (the uppermost layer) from the wire-accommodatingportion of the first layer (the bottom layer).

Next, the winding process from the second circle of the winding wireportion 2 b of the second layer (the uppermost layer) to the secondcircle of the winding wire portion 2 a of the first layer (the bottomlayer) will be explained. In this process, the winding process forforming the second circle of winding wire b2 in the winding wire portion2 b of the second layer (the uppermost layer) is performed at first, andthen the winding process for forming the second circle of winding wirea2 in the winding wire portion 2 a of the first layer (the bottom layer)is performed. As such, a single turn of winding is performed from theuppermost layer to the bottom layer in sequence, and thereby a circle ofwinding wire is formed in the winding wire portion of each layer.Hereinafter, this process is referred to as the second winding process,and the part formed in the second winding process becomes the secondwinding portion in which a single turn of winding is performed for eachlayer in the same winding direction from the uppermost layer to thebottom layer. Further, when the wire 2 is moved from the second circlein the winding wire portion 2 b of the second layer (the uppermostlayer) to the second circle in the winding wire portion 2 a of the firstlayer (the bottom layer), it passes through a slit 3 provided in theplate portion 1 b and enters into the wire-accommodating portion of thefirst layer (the bottom layer) from the wire-accommodating portion ofthe second layer (the uppermost layer).

In this way, the first circle of winding wire a1 in the winding wireportion 2 a of the first layer (the bottom layer) and the first circleof winding wire b1 in the winding wire portion 2 b of the second layer(the uppermost layer) are formed by performing the first windingprocess, and then the second circle of winding wire b2 in the windingwire portion 2 b of the second layer (the uppermost layer) and thesecond circle of winding wire a2 in the winding wire portion 2 a of thefirst layer (the bottom layer) are formed by performing the secondwinding process. Similarly below, the first winding process and thesecond winding process are repeated alternatively so that the third tosixth circle of winding wires a3 to a6 in the winding wire portion 2 aof the first layer (the bottom layer) and the third to sixth circle ofwinding wires b3 to b6 in the winding wire portion 2 b of the secondlayer (the uppermost layer) are formed. The thus formed winding wireportion 2 a of the first layer (the bottom layer) and the winding wireportion 2 b of the second layer (the uppermost layer) become windingwire portions that are wound 6 circles in a plane. The planar windingwire portion 2 a faces the winding wire portion 2 b via the plateportion 1 b.

As described above, the coil with a double layered structure shown inFIG. 3 and FIG. 4 according to the second embodiment is formed byperforming the first winding process and the second winding process eachfor three times. In other words, the first circle of winding wire a1 inthe winding wire portion 2 a of the first layer (the bottom layer) andthe first circle of winding wire b1 in the winding wire portion 2 b ofthe second layer (the uppermost layer) are formed by performing thefirst winding process for the first time, and then the second circle ofwinding wire b2 in the winding wire portion 2 b of the second layer (theuppermost layer) and the second circle of winding wire a2 in the windingwire portion 2 a of the first layer (the bottom layer) are formed byperforming the second winding process for the first time. Then, thethird circle of winding wire a3 in the winding wire portion 2 a of thefirst layer (the bottom layer) and the third circle of winding wire b3in the winding wire portion 2 b of the second layer (the uppermostlayer) are formed by performing the first winding process for the secondtime, and then the fourth circle of winding wire b4 in the winding wireportion 2 b of the second layer (the uppermost layer) and the fourthcircle of winding wire a4 in the winding wire portion 2 a of the firstlayer (the bottom layer) are formed by performing the second windingprocess for the second time. Next, the fifth circle of winding wire a5in the winding wire portion 2 a of the first layer (the bottom layer)and the fifth circle of winding wire b5 in the winding wire portion 2 bof the second layer (the uppermost layer) are formed by performing thefirst winding process for the third time, and then the sixth circle ofwinding wire b6 in the winding wire portion 2 b of the second layer (theuppermost layer) and the sixth circle of winding wire a6 in the windingwire portion 2 a of the first layer (the bottom layer) are formed byperforming the second winding process for the third time.

The winding wire portions 2 a and 2 b may also be wound in any one ofshapes such as a circle, an oval, a substantial quadrangle or the like.In addition, the location where the slit is provided is not particularlyrestricted, but it is preferred that the slit is provided around thebending part (the angle part when wound to be substantiallyquadrangular) of the wire 2. The thickness of the plate portion 1 b ispreferably decided by the closing effect, and the angle of the slit 3(which is provided in the plate portion 1 b) to which the wire 2 abutsis preferably to be chamfered as shown in FIG. 5 (the part surrounded bythe circle 4 refers to the part which is chamfered). The Litz wire ispreferably used as the wire 2. Further, a wire obtained by covering theLitz wire with an insulating tube may also be used as the wire 2.

Hereinafter, the winding process for forming the winding wire portion ina coil with a three layered structure will be explained with referenceto FIG. 6. FIG. 6 is a sectional view of the coil with a three layeredstructure, and the coil with a three layered structure is provided witha winding wire portion 2 a of the first layer (the bottom layer), awinding wire portion 2 b of the second layer and a winding wire portionof the third layer 2 c (the uppermost layer). Similar to the coil with adouble layered structure shown in FIG. 3 and FIG. 4, the coil with athree layered structure is also formed by performing the first windingprocess and the second winding process each for three times.

Firstly, with the first winding process, the winding processes forforming the first circle of winding wire a1 in the winding wire portion2 a of the first layer (the bottom layer), the first circle of windingwire b1 in the winding wire portion 2 b of the second layer and thefirst circle of winding wire c1 in the winding wire portion 2 c of thethird layer (the uppermost layer) are performed in sequence. Then, withthe second winding process, the winding processes for forming the secondcircle of winding wire c2 in the winding wire portion 2 c of the thirdlayer (the uppermost layer), the second circle of winding wire b2 in thewinding wire portion 2 b of the second layer and the second circle ofwinding wire a2 in the winding wire portion 2 a of the first layer (thebottom layer) are performed in sequence. Similarly below, the firstwinding process and the second winding process are repeatedalternatively so that the third to sixth circle of winding wires a3 toa6 in the winding wire portion 2 a of the first layer (the bottomlayer), the third to sixth circle of winding wires b3 to b6 in thewinding wire portion 2 b of the second layer and the third to sixthcircle of winding wires c3 to c6 in the winding wire portion 2 c of thethird layer (the uppermost layer) are formed. The thus formed windingwire portion 2 a of the first layer (the bottom layer), the winding wireportion 2 b of the second layer and the winding wire portion 2 c of thethird layer (the uppermost layer) become winding wire portions that arewound 6 circles in a plane.

As such, in the case involving the coil with a three layered structure,the winding wire portion in each layer can also be formed byalternatively repeating the first winding process and the second windingprocess. In addition, in the structure with three layers, a slit is alsoprovided in the plate portion 1 c. The slit provided in the plateportion 1 c is arranged in a position substantially the same as that ofthe slit provided in the plate portion 1 b. That is, when viewed in adirection perpendicular to the plate portion 1 c, the slit provided inthe plate portion 1 c and the slit provided in the plate portion 1 b aresubstantially coincide in position.

Further, when the coil has a structure with four or more layers, thewinding wire portion of each layer can also be formed by alternativelyrepeating the first winding process and the second winding process. Thenumber of circles formed in the winding wire portion of each layer canbe changed in accordance with the repeating times of the first windingprocess and the second winding process. For example, when the number ofcircles in the winding wire portion of each layer is set to be 8, thefirst winding process and the second winding process are respectivelyperformed for four times. When the number of circles in the winding wireportion of each layer is set to be 9, the first winding process isperformed for another time after the first winding process and thesecond winding process are respectively performed for four times.Further, if the circle number is to be differed among the winding wireportions of each layer, the winding process for the winding wire portionof which the circle number is to be decreased should be skipped (forexample, after the winding process for the first layer, the windingprocess continues on the third layer with the winding process omittedfor the second layer) or the winding process for the outmost circle isstopped halfway.

Then, the contactless power transmission circuit according to thepresent invention in which the coil with a multilayered structure isused as a coil for transmitting power or a coil for receiving power willbe explained with reference to FIG. 7. In FIG. 7, the principle circuitwhich is connected to the power transmitting coil and the principlecircuit which is connected to the power receiving power are shown. Thedriving circuit for supplying an alternating current to the powertransmitting coil Lt is composed of switching elements SW1 to SW4. Theswitching element SW1 and the switching element SW2 are connected inseries, and an input voltage Vin is applied to both ends. Similarly, theswitching element SW3 and the switching element SW4 are connected inseries, and an input voltage Vin is applied to both ends. The powertransmitting coil Lt has one end connected to one end of the capacitorCt1 and the other end connected to one end of the capacitor Ct2. Theother end of the capacitor Ct1 is connected to the junction between theswitching element SW1 and the switching element SW2, and the other endof the capacitor Ct2 is connected to the junction between the switchingelement SW3 and the switching element SW4. The current flowing throughthe power transmitting coil Lt is controlled by the on-off state of theswitching elements SW1 to SW4.

The power receiving circuit for supplying the power received by thepower receiving coil Lr to the load is composed of a bridge diode Dr anda capacitor Co. The power receiving coil Lr has one end connected to oneend of the capacitor Cr1 and the other end connected to one end of thecapacitor Cr2. The other end of the capacitor Cr1 is connected to oneinput of the bridge diode Dr, and the other end of the capacitor Cr2 isconnected to the other input of the bridge diode Dr. The capacitor Co isconnected between the output terminals of the bridge diode Dr. Thecurrent flowing through the power receiving coil Lr is full-waverectified by the bridge diode Dr and is then provided to the capacitorCo.

Then, the switching operation of the switching elements SW1 to SW4 willbe explained. For example, the period during which the switching elementSW1 and the switching element SW4 are on and the switching element SW2and the switching element SW3 are off, and the period during which theswitching element SW1 and the switching element SW4 are off and theswitching element SW2 and the switching element SW3 are on will bealternatively repeated. The voltage Vdr between the junction of theswitching element SW1 and the switching element SW2 and the junction ofthe switching element SW3 and the switching element SW4 (the voltagedeems the side where the junction between the switching element SW3 andthe switching element SW4 is located as the reference) changes based onthe on-off state of the switching elements SW1 to SW4. When theswitching element SW1 and the switching element SW4 are on and theswitching element SW2 and the switching element SW3 are off, the voltageVdr has a positive voltage value with its absolute value equal to thatof the input voltage Vin. On the other hand, when the switching elementSW1 and the switching element SW4 are off and the switching element SW2and the switching element SW3 are on, the voltage Vdr has a negativevoltage value with its absolute value equal to that of the input voltageVin.

The alternating current based on the alternating voltage Vdr flowsthrough the power transmitting coil Lt and thereby the powertransmitting coil Lt will generate a magnetic field. At that time, thealternating current which is based on the magnetic field generated bythe power transmitting coil Lt flows through the power receiving coilLr, and the current is full-wave rectified by the bridge diode Dr and isthen supplied to the capacitor Co.

Next, an example in which the coil with a multilayered structure of thepresent invention is used as the power transmitting coil Lt or the powerreceiving coil Lr shown in FIG. 7 will be explained with reference toFIG. 8 and FIG. 9. FIG. 8 and FIG. 9 are sectional views showing thepower transmitting coil and the power receiving coil both of which areoppositely disposed. In FIG. 8, both the power transmitting coil Lt andthe power receiving coil Lr are composed of one coil, and in FIG. 9,both the power transmitting coil Lt and the power receiving coil Lr arecomposed of two coils.

In the example of FIG. 8, a coil 11 with a double layered structure isused to form the power transmitting coil 10, and a coil 21 with a doublelayered structure is used to form the power receiving coil 20. The powertransmitting coil 10 is composed of the coil 11, a magnetic member 12and a metallic plate 13. The magnetic member 12 and the metallic plate13 are disposed in sequence at the opposite side of the coil 11 the sideof which faces the coil 21. The power receiving coil 20 is composed ofthe coil 21, a magnetic member 22 and a metallic plate 23. The magneticmember 22 and the metallic plate 23 are disposed in sequence at theopposite side of the coil 21 the side of which faces the coil 11. Thesemetallic plates 13 and 23 are composed of an aluminum plate or a copperplate.

If such a structure is used in the contactless power transfer, thebalance of the parasitic capacitance in the coil will deteriorate sothat the voltage to ground of the metallic plate 13 or the voltage toground of the metallic plate 23 will increase. However, in the coil witha multilayered structure according to the present invention, since thebalance of the parasitic capacitance is good, the voltage to ground ofthe metallic plate 13 or the voltage to ground of the metallic plate 23can be prevented from increasing.

In the example of FIG. 9, the coils 31 a and 31 b both with a doublelayered structure are used to constitute the power transmitting coil 30,and the coils 41 a and 41 b both with a double layered structure areused to constitute the power receiving coil 40. The power transmittingcoil 30 is composed of the coils 31 a and 31 b, a magnetic member 32 anda metallic plate 33. The magnetic member 32 and the metallic plate 33are disposed in sequence at a side of the coils 31 a and 31 b which sideis opposite to that facing the coils 41 a and 41 b. The power receivingcoil 40 is composed of the coils 41 a and 41 b, a magnetic member 42 anda metallic plate 43. The magnetic member 42 and the metallic plate 43are disposed in sequence on a side of the coils 41 a and 41 b which sideis opposite to that facing the coils 31 a and 31 b. In addition, thedirection of the magnetic field generated by the coil 41 a and thedirection of the magnetic field generated by the coil 41 b are set to beopposite to each other. These metallic plates 33 and 43 are composed ofan aluminum plate or a copper plate.

The coil 41 a and the coil 41 b are connected to each other via the endsextending from the winding wires on the outermost periphery. With such aconnection, even if the winding wires of the coil 41 a and the coil 41 bon the outermost periphery are close to each other to lower the voltagedifference between these two coils, no special means for voltageprotection is needed. Further, similar to the situation in the powertransmitting coil 10 and the power receiving coil 20, the voltage toground of the metallic plate 33 or the voltage to ground of the metallicplate 43 can be prevented from increasing.

The embodiments of the coil with a multilayered structure of the presentinvention have been described above, but the present invention is notlimited to these embodiments described above and various modificationscan be applied without departing from the spirit. For example, withrespect to the layer number of the multilayered structure and the circlenumber of the winding wire portion in each layer, the coil can beconstituted with various combinations. However, it is preferable thatthe number of the circles of the winding wire portion in each layer islarger than the number of the layers in the multilayered structure. Inaddition, with respect to the wire, wire materials other than the Litzwire can be used.

What is claimed is:
 1. A coil with a stacked structure which comprises awinding wire portion formed of a wire wound multiple times in a plane ineach layer, wherein the winding wire portion in each layer includes afirst winding portion formed by performing a single turn of winding ineach layer in a same winding direction from a bottom layer to anuppermost layer and a second winding portion formed by performing asingle turn of winding in each layer in a same winding direction fromthe uppermost layer to the bottom layer, and the winding directions ofthe first winding portion and the second winding portion are identicalto each other, and the first winding portion and the second windingportion are joined in the uppermost layer or the bottom layer.
 2. Thecoil of claim 1, wherein, the winding wire portions in the adjacentupper and lower layers face each other via an insulating member.
 3. Thecoil of claim 2, wherein, the insulating member is a planar memberprovided with a slit, and the wires of the winding wire portion in theadjacent upper and lower layers are joined via the slit.